Hermetically sealed electrical connectors and method of producing same



A rifz- 1964 R. M. GRAY 3,130,260 HERMETICALLY SEALED ELECTRICAL CONNECTORS AND METHOD OF PRODUCING SAME Filed April 2, 1962 2 Sheets-Sheet 1- FIG. I. -FIG. 2; FIG. 6.

INVENTOR Y ROLAND M. GRAY ATTORNEYS.

P 1964 R. M. GRAY 3,130,260

HERMETICALLY SEALED ELECTRICAL CONNECTORS AND METHOD OF PRODUCING SAME Filed April 2, 1962 2 Sheets-Sheet 2 FIG. 1/.

FIG. I2.

INVENTOR ROLAND M. GRAY Y [W wL W ATTORNEYS Un ted States Patent Oflice 3,130,260 Patented Apr. 21, 1964 3,13%,260 HERMETHCALLY SEALED lELEQTRICAL CQNNEC- TOR AND METHEED @F PRDDUCING SAME RolaudM. Gray, Newark, Deh, assignor to Tri-Point gldtllftiles, Inc, Alhertson, N.Y., a corporation of New Filed Apr. 2, 1962, Ser. No. 134,375 g '10 Claims. (Cl. 174-152) This invention relates to electrical connectors or electrical wiring assemblieswherein one or more metallic pins or other conductors are encapsulated in an insulating base and are preferably hermetically sealed thereto. More particularly, the present invention relates to the novel method of producing such electrical connectors and wiring assemblies, as well as to the novel electrical connectors and assemblies produced thereby.

In connection with electrical wiring there is presently in use a large number of types of connectors, terminals and the like which serve as supports, junctions, and connection points for electrical wiring. Most of these devices comprise three essential elements, i.e.:

(1) A main body which is usually of a metallic material such as brass, steel, aluminum, or the like;

(2) Metallic pins passing through an encapsulating core material, such pins usually being of an electrical conductive metal such as copper, aluminum, steel, or the like; and

i (3) A cored section of an electrical insulating type of material which very often is an encapsulating material such as glass, which is used as the insulating material around the pins. 7

One of the disadvantages of electrical connectors of the type mentioned is that it is difiicult to maintain firmness of seal when they are subjected to repeated temperature cycling, as the three components have varying coeflicients of thermal expansion which operate in varying directions. Thus it has been found that with repeated temperature cycling, relative movement of the components gives rise to leakage.

It has also been found that with connectors of the above described type, utilizing a rigid non-yielding, breakable type of encapsulating or insulating material, such as glass, vibration will cause chipping, breaking, or loosening of such encapsulating material, and will give rise to loss of sealing function.

It has also been found that when the connector is composed of three separates types of elements, two of which are usually metallic and one of which is usually glass, with none of these three types of materials being chemically inert, such different materials tend to widen the field of corrosive conditions which contribute to deterioration of the composite unit.

It is the primary object of the present invention to provide electrical assemblies and electrical connectors which overcome the shortcomings of the prior art and which maintain a good seal at all times irrespective of temperature cycling and vibrational forces, and which are substantially inert to deleterious corrosive action.

.In practicing the present invention, advantage is taken of the known characteristics of polytetrafluoroethylene which is a plastic material put out by E. I. du Pont de Nemours & Co. under the trademark Teflon. For convenience, throughout this specification this material will be referred to as TFE-Teflon which is the designation adopted by the Society of Plastics Industry.

In practicing the present invention advantage also is taken of the known characteristics of a fluorinated ethylene propylene plastic material, also put out by E. I. du Pont de Nemours & Co. under the trademark Teflon. For convenience, throughout this specification this material will be referred to as PEP-Teflon, which is the designation adopted by the Society of Plastics Industry.

It has a high temperature resistance; excellent electrical insulating properties; inertness to chemical attack; zero moisture absorption; and good serviceability over a wide range of temperatures. In addition, although it is classified as a thermoplastic resin, it is not a true thermoplastic material for the reason that it does not melt under high temperatures into a fluid or molten state as do most conventional thermoplastics. On the contrary, according to known processing techniques TFE-Teflon or polytetrafluoroethylene raw material powders are converted into finished stock or custom shapes by processes which include the essential steps of: (a). compacting the raw material powders under pressure and (b) then sintering the compacted material at an elevated temperature into a fused solid article. During the sintering step, as the compacted article is heated through a temperature of approximately 625 F. it passes into a gel condition. This temperature is usually referred to as the melt transition point of polytetrafluoroethylene, although the material does not pass into a fluid state. As the temperature is further raised above 625 F. to approximately 700 F. the polytetrafiuoroethylene remains in this gel condition. When cooled from 700 F. through the 625 F. transition temperature, the polytetrafiuoroethylene by virtue of the sintering process, has become converted into a usable fused article. It is also well known that such a sintered product can again be reheated to the gel temperature range of 625 F. or above and again be cooled without any harmful effect.

Another of the known characteristics ofTFE-Tefion shapes or parts which are produced according to the foregoing process'is that such shapes or parts retain permanently a type of plastic memory. It has been found that any manufactured component of TFE-Teflon has a fundamental relaxed or stress-free position and that this position is the original natural position in which the raw material powder particles Were compacted prior to the sintering stage of manufacture. 'Any TFE-Teflon shape which has been sintered and is then allowed to cool from the elevated sintering temperature, if unrestrained by outside forces will retain or assume the position or shape which it had when originally compacted. Such stress free or relaxed shapes or parts then retain permanently the type of plastic memory referred to which can be defined as a latent desire (when exposed to heat) to remain in or return to the original position in which the raw material particles were compacted before sintering. Such a shape or part which is moved by exterior forces from its stress-free or relaxed position will, when exposed to elevated temperatures, exert a definite desire and force to return to its above described stress-free position. This returning force only takes effect when the shape orpart is exposed to elevated temperatures and little or no such force is exerted unless the article is so exposed to such elevated temperatures.

The characteristics of PEP-Teflon or fluorinated ethylene propylene which are availed of according to the present invention are the following: I g This material exhibits, with minor exceptions, the same highly useful combination of properties of TFE-Teflon discussed above. However, the process methods by which it is manufactured into articles are substantially different from those for TFE-Teflon since this material is a true thermoplastic and when exposed to elevated temperaturet' passes into an actual molten state. PEP-Teflon begins to soften toward its molten state at a temperature of approximately 525 F. and becomes increasingly fluid up to temperatures of 650 F. to 700 F.

In evolving the present invention there has also been taken into account the fact that in the electrical, electronic, aircraft, missile and other industries extensive use is made of electrical wiring which is TEE-Teflon covered because of its excellent electrical insulating qualities and the wide ranges of temperature over which it can successfully operate.

According to the present invention, in its simplest form, an electrical connector having one or more TEE-Teflon insulated conductive wires mounted in an insulating base and hermetically sealed therein, is provided by practicing the following method:

(a) A TFE-Teflon base member in relatively stressfree or relaxed condition is first prepared either by molding according to the foregoing outline or by being machined from a section of a TFE-Teflon rod.

(b) A series of holes are then drilled in such base member of approximately the same size or slightly larger than the size of the insulated wires to be inserted therein.

(c) A series of small tubes or sleeves are prepared to encompass portions of the insulated wire, such tubes or sleeves being made from PEP-Teflon.

(d) The holes in the base member are then mechanically enlarged, without cutting, by forcing tapered pins or other enlarging means into the holes to give each of them a diameter large enough to receive an insulated wire with a PEP-Teflon sleeve mounted thereon, with each sleeve positioned in one of such holes.

(e) The entire assembly is then heated to a temperature above the melt transition point of TIRE-Teflon and is held at this temperature for a suitable period of time. During this heating step and while at temperatures well below the melt transition point the TFE-Teflon base tends to restore to its original condition and the holes (which were mechanically enlarged) tend to reduce to their original diameter. This develops an inwardly acting force adjacent the PEP-Teflon sleeves which increases as the temperature increases. When the temperature reaches the temperature at which PEP-Teflon becomes fluid, the inwardly acting forces thin out and extrude some of the sleeve material and also serve to achieve a bond between the Teflon surfaces.

The entire assembly is then permitted to cool, and during such cooling the base member remains under stress and continues to exert a tightening force against the sleeves and insulated wires and thereby provides an excellent hermetic seal, for the reason that the sleeves and the wires still do not permit the holes in the base to return completely to their original diameter.

Reference will now be made to the accompanying drawings wherein the preferred embodiments of the pres ent invention are illustrated. In these drawings an effort has been made to parallel by separate figures the steps of the process as outlined above.

FIGURE 1 is a side elevational view, and FIG. 2 is an end elevational view, of a TFE-Teflon base member in stress-free or relaxed condition with a series of holes drilled therein;

FIG. 3 is a side elevational view of a PEP-Teflon sleeve of larger diameter than the holes shown in FIG. 2;

FIG. 4 is a side elevational view of a TFE-Teflon insulated conductive wire of a diameter approximately the same as the diameter of the holes shown in FIG. 2;

FIG. 5 is a side elevational view of a tapered pin for mechanically enlarging the holes shown in the base member of FIG. 2;

FIG. 6 is a view corresponding to FIG. 2 but showing in full line the holes after enlargement as contrasted with the holes before enlargement as shown in dotted line;

FIG. 7 shows a side elevation of the T FE-Teflon insulated wire with the FEP-Tefion sleeve applied thereto;

FIGS. 8 and 9 show a side elevation and an end elevation, respectively, of the conductor assembly after the insulated wires with sleeves have been inserted in the enlarged holes provided in the base member of FIGS. 1 and 2;

FIG. 10 is a perspective view of the finished conductor assembly after it has been heated and then cooled to provide a weldment of the base member, the sleeves and the insulated wires.

FIG. 11 shows in end elevation one modified form of the invention; and

FIG. 12 shows in side elevation, and FIG. 13 shows in end elevation another modified form of the invention.

Referring now to the drawings in more detail, in order to facilitate comprehension of the present invention, more or less precise dimensions for the disclosed preferred embodiment will be given. It will be understood, however, that these dimensions are only illustrative and are not intended to limit the scope of the present invention.

In the drawings 14) is a base member formed from TFE-Teflon or polytetraliuoroethylene which was machined from a section of a rod prepared according to the method heretofore outlined, which includes the steps of pressure molding or extruding and sintering so as to be in a relatively relaxed or stress-free condition. This base member has a flange ill and a main body 12. A plurality of through holes 13 are provided in such base member, preferably by drilling. In one commercial embodiment the main body 12 is approximately inch diameter and inch in length, exclusive of the flanged portion. The flange portion ll. is approximately inch thick with its dimensions being approximately W inch wide by inch long. In the embodiment shown in FIGS. 1 and 2 eight holes 13 have been provided of approximately .046 inch in diameter.

An insulated wire 15 shown in FIG. 4 comprises a metal conductive element 16 and a TPE-Teflon insulating covering 17. In the commercial embodiment being described the outside diameter of the insulated wire was approximately .044 inch. Eight of such wires, would be provided, one for each hole in the base member 10, and normally each of these wires would be of a different color to facilitate identification for wiring into the circuit in which the conductor is used.

A sleeve 20 as shown in FIG. 3, is provided for each wire 15, said sleeve being composed of PEP-Teflon or fluorinated ethylene propylene or other plastic having sub stantially the same characteristics. While in the preferred embodiment of the invention the sleeve 2% is cut from PEP-Teflon tubing, it will be understood that the equivalent of such a sleeve can be attained by utilizing dispersion material or sections cut from PEP-Teflon film or sheet material. In the one commercial embodiment noW being described the sleeve has an outside diameter approximately .062 inch and an inside diameter approximately .046 inch and a length of approximately 7 inch to /2 inch. It will thus be noted that a clearance is provided for such sleeve to be slipped over the insulated wire 15, and that the outside diameter of both the sleeve and the wire of .062 inch considerably exceeds the diameter of the holes 13 drilled in the base member 10. One sleeve 20 is provided for each of eight wires 15.

A tapered pin 22 as shown in FIG. 5 is utilized according to the present invention to enlarge the holes 13 in the base member 10. In the one commercial embodiment now being described this tapered metal pin 22 is approximately 2 /2 inches long, has at its main body 23 a maxi mum diameter of .068 inch and has a minimum diameter at one end (24) of approximately .040 inch, with the, taper extending about 1 inch inwardly from said end..

Tapered pins 22 are then forced into the holes 13 in the basemember l so as to enlarge the samewithout cutting until the main body 23 of each said tapered pin is located within such hole and the latter hence has been enlarged through the cold-flow nature of the sintered TFE- Teflon to substantially the same diameter as the main body of such tapered pin, i.e., .068 inch. 0 When the pins are removed the holes remain substantially in such enlarged condition. In the commercial embodiment being described it was found that they retained a diameter of approximately .060 inch to .065 inch. FIG. 6 of the drawings shows in full line holes 13 of enlarged diameter and in dotted line the same holes of original diameter.

The wires 15 with the PEP-Teflon sleeves 20 are then inserted within the enlarged holes 13 with the sleeves axially centered within the holes and with the wires extending at predetermined distances on each side of the base member depending upon the place where it is desired to have such wires sealed in such base member. In the commercial embodiment being described it will be noted that the outside diameter of the wire plus sleeve of approximately .062 inch may be easily slipped into the enlarged yhole having a diameter of approximately .062 inch to .067 inch.

-With the assembly thus arranged as shown in FIGS. 8 and 9 of the drawings, the entire unit is ready to be subjected to a heating cycle and the entire assembly heated to a temperature above the melt transition point of THE- Teflon for a suflicient period of time to insure that the elevated temperature permeates the entire assembly (sometimes called soaking). In practice, it has been found that if the entire assembly is placed in an electrically heated oven, heated to a temperature of 640 F. and maintained at this temperature for a period of approximately minutes, satisfactory results I were obtained. I n

The cycle of heating and soaking has been found to accomplish certain actions which after completion and cooling give rise to an assembly which is an integral sealed unit.

Further fabrication of the assembly may then be done, such for instance as drilling or punching holes in the flanged portion 11, trimming or machining the dimensions of the body'iZ or the flange ll, or trimming the ends of the wires 15, so as to complete the final assembly.

It will be understood that during the fabrication of the assembly as thus described, as aresult of mechanically enlarging the diameter of holes 13 they change from a relaxed or stress-free condition to a moved or altered condition and that when the base member 10 is exposed to elevated temperatures the material around these holes will exert a force tending to return them to their original diameters and their original stress-free condition. At the gel temperature the TFE-Teflon surrounding these holes would, if unrestricted, return completely to a stress-free position.

It will also be understood that the sleeves which are made of PEP-Teflon will begin to soften at a temperature of approximately 525 F. and will be in a molten state at temperatures of approximately 600 F. It Will also be understood that the PEP-Teflon may be bonded to the TFE-Teflon if the two materials are subjected to elevated temperatures and if pressure is maintained between the two materials while at elevated temperatures.

Thus, accordingto the present invention the forces exerted by the body portion 12 surrounding the enlarged holes 13 which are exertedin an inward direction to cause said holes to try to assume their original diameter or position are exerted on both the sleeve 20 while it is in a molten state and on the insulation 1'7 for the wire 15 to such an extent that there is in eifecta bond or Weld between. the

form globules 26 Pro. 10 These globules which re main around the wires at the ends of the holes 13 also serve as an additional sealing means.

It will be understood by virtue of the fact that the holes 13 in the base member 10 are not permitted by the sleeve 20 and insulated wire 13 to return fully to their original diameter or position, that the material surrounding such holes is not stress-free and continues to exert an inward acting force against such sleeve and insulated Wire. This force will continue irrespective of how many times the assembly is raised to elevated temperatures and then cooled. Thus the present invention not only provides an excellent bond orweldment between the base member, the sleeves, and the insulated wires, but also provides an improved hermetic seal which has been found to be extremely reliable and effective in functional operation.

It should particularly be noted that if the assembly is subjected to repeated exposure to heating and cooling there are no thermal expansion forces which work against retention of the seal. In fact, it might be said that there is an annulment or cancellation of thermal expansion forces at the critical sealing points.

While the invention has thus far been described with reference to one commercial embodiment, it will be understood that it is not so limited. Hence, there is shown in FIG. 11 a modified form wherein the base member 30 is of considerably larger size than base member 10 and has the additional features that in addition to a plurality of holes 33 for individual insulated wires, there is a hole 34 of such configuration as to receive a plurality of insulated wires 35 such as the three shown. This base member is also provided with counterbored holes 36 where the wire may be soldered directly within the counterbored hole or may be attached to a wiring attachment such as a female electrical terminal plug installed within such counterbored section.

FIGS. 12 and 13 show a further modification of the invention wherein a plurality of TEE-Teflon insulated wires'in the form of a connected multiple conductor ribbon 40 and an enveloping sleeve ll have been similarly hermetically sealed in a correspondingly formed slot 42 which prior to sealing had been mechanically enlarged in accordance with the foregoing disclosure.

From the foregoing description it will be understood that the present invention provides electrical connector wiring assemblies which eliminate the necessity for soldered connections; which provide a very substantial reductionin over-all weight as compared to the weight of metallic-glass type of connectors; which provide better electrical insulation advantages because no metallic material is necessary in the mounting section; and which also permits of space-saving as smaller over-all sized units can be used because of the superior electrical insulating qualities afforded.

It will also be understood that in its broader form the invention contemplates the use of metallic pins and bare wires which are not TFE-Teflon insulated. In such instance suoh pins or bare wires will be provided with PEP-Teflon sleeves in the same manner as heretofore described. While this construction would provide definite advantages over metallic-glass connectors, it would not provide the degree of weldment which is achieved when the conductor is TFE-Teflon insulated.

What I claim is:

1. The method of securing a first member of predetermined oross-sectional dimension and shape in a plastic base member having the characteristics of polytetrafluoroethylene, comprising the steps of encompassing the first member with plastic covering and to cause the base member to be in a stressed condition, inserting said first member with plastic covering in said enlarged hole with said plastic covering disposed within said hole, heating the entire assembly to the gel temperature of said base member, and then cooling the same, whereby there is provided -a substantially hermetic seal between said members.

2. The method of producing a hermetically sealed electrical connector comprising the steps of applying a sleeve of fiuorinated ethylene propylene to an insulated electrical conductor, forming a base member of unstressed polytetrafluoroethylene with at least one hole therein of a dimension smaller than the cross-sectional dimension of the said insulated electrical conductor and sleeve, enlarging by mechanical expansion means the hole in such base member to a cross-section slightly larger than the cross-section of the said insulated electrical conductor and sleeve to cause the base member to be in a stressed condition, inserting within said enlarged hole the insulated electrical conductor with the sleeve of fiuorinated ethylene propylene thereon, exposing the entire unit to an elevated temperature above 500 F, and allowing the entire unit to cool to a temperature below 00 R, whereby said base member snugly engages said sleeve and conductor under stressed conditions.

3. The method of producing a hermetically sealed electrical connector comprising the steps of applying sleeves of fluorinated ethylene propylene to polytetrafiuoroethylene insulated electrical conductors forming a base member of unstressed polytetrafluoroethylene with a plurality of holes therein each of a dimension smaller than the cross-sectional dimension of the said insulated electrical conductors and sleeves, enlarging by mechanical expansion means each hole in said base member to a crosssection slightly larger than the cross-sectional dimension of the said insulated electrical conductors and sleeves, to cause the base member to be in a stressed condition, inserting within each such enlarged hole one of the said polytetrafluoroethylene insulated electrical conductors having the sleeves of fluorinated ethylene propylene thereon, exposing the entire assembly to an elevated temperature above 500 F. until said base member attains a state of gel and said fluorinated ethylene propylene sleeves become molten, and allowing the entire assembly to cool to a temperature below 500 F., whereby said base member exerts an inward force against said sleeves and said insulated conductors and efiectively provides a weldment of the same.

4. The method of producing a hermetically sealed electrical connector comprising the steps of providing on each of a plurality of polytet-rafiuoroethylene-covered insulated wires a sleeve of fluorinated ethylene propylene, forming a base member of unstressed polytetratluoroethylene with a plurality of holes therein corresponding to the number of wires, with each hole being of a crosssectional dimension smaller than the cross-sectional dimension of the insulated wire with sleeve thereon, enlarging by mechanical expansion means each of said holes in the base member to a cross-sectional dimension slightly larger than the cross-sectional dimension of the wire and sleeve to be inserted therein to cause the base member to be in a stressed condition, inserting said wires and sleeves within said holes with the sleeves substantially contained within the said holes, heating the entire assembly to the gel temperature of polytetrafluoroethylene until the heat at such temperature permeates the entire assembly, and allowing the assembly to cool to a temperature below 500 F., whereby said base section engages said sleeves and conductors under stressed conditions and a (3 C3 weldment is provided with said base member, sleeves and insulated coverings.

5. A connector comprising a base member having plastic memory characteristics of sintered polytetrafluoroethylene, said base member having a through hole therein, an electrical conductor part disposed within the hole in said base member of the same general cross-sectional shape and dimension as said hole and extending beyond the faces of said base member, and a plastic material having the characteristics of fiuorinated ethylene propylene distributed between said base member and part within the hole, the material around said hole in said base member being under stress and exerting forces against the said plastic material and the part contained therein to maintain the same in tight engagement.

6. An electrical connector comprising a base member aving the plastic memory and insulating characteristics of sintered polytetrafluoroethylene, said base member having at least one through hole therein, an electrical conductor disposed within said hole and a plastic material having the characteristics of fluorinated ethylene propylene distributed between said base member and conductor within each hole, said base member in the area surrounding said conductor being under stress and exerting a force against said plastic material and said electrical conductor to maintain the same in tight engagement.

7. An electrical connector comprising a base member having the plastic memory and insulating characteristics of ,sintered polytetrafiuoroethylene, said base member having a plurality of through holes therein, an electrical conductor disposed within each said hole, and a plastic material having the characteristics of fluorinated ethylene propylene distributed between said base member and each conductor within each hole, said base member in the areas surrounding said conductors being under stress and exerting forces against said plastic material and said electrical conductors to maintain the same in tight engagement.

8. An electrical connector comprising a base member having the plastic memory and insulating characteristics of sintered polytetrafluoroethylene, said base member having a plurality of through holes therein, a polytetrafluoroethylene covered wire disposed within each said hole, and a plastic material having the characteristics of fluorinated ethylene propylene distributed between said base member and each wire within each hole and extending beyond said base member on each side thereof, said base member in the area surrounding said wires being under stress and exerting forces against said plastic material and said polytetrafluoroethylene covering on said wires to maintain the same in tight engagement with said base.

9. A hermetically sealed electrical connector comprising a base member having the plastic memory and insulating characteristics of sintered polytetrafluoroethylene, said base member having a plurality of through holes therein, a fluorinated ethylene propylene sleeve disposed in each of said holes, and a polytetrafluoroethylene covered wire disposed in each of said sleeves with the wires extending beyond said base member on each side thereof, said base member in the area surrounding said sleeves and covered wires being under stress and exerting forces against said sleeves and wire coverings to maintain the same tightly bonded.

10. A hermetically sealed electrical connector according to claim 9 wherein enlarged globules are provided on each end of each fluorinated ethylene propylene sleeve.

References Cited in the file of this patent FOREIGN PATENTS 484,849 Canada July 15, 1952 

6. AN ELECTRICAL CONNECTOR COMPRISING A BASE MEMBER HAVING THE PLASTIC MEMORY AND INSULATING CHARACTERISTICS OF SINTERED POLYTETRAFLUOROETHYLENE, SAID BASE MEMBER HAVING AT LEAST ONE THROUGH HOLE THEREIN, AN ELECTRICAL CONDUCTOR DISPOSED WITHIN SAID HOLE AND A PLASTIC MATERIAL HAVING THE CHARACTERISTICS OF FLUORINATED ETHYLENE PROPYLENE DISTRIBUTED BETWEEN SAID BASE MEMBER AND CONDUCTOR WITHIN EACH HOLE, SAID BASE MEMBER IN THE AREA SURROUNDING SAID CONDUCTOR BEING UNDER STRESS AND EXERTING A FORCE AGAINST SAID PLASTIC MATERIAL AND SAID ELECTRICAL CONDUCTOR TO MAINTAIN THE SAME IN TIGHT ENGAGEMENT. 